A method of providing a buffer pool on a database server for temporarily storing contents of a database for the purpose of increasing the speed of access to the database has been used. Ordinarily, the effect of increasing the access speed is higher in the case of providing a plurality of buffer pools on a database in correspondence with types of transaction than in the case of providing one buffer pool on the database.
In a case where the total size of a memory area usable as a buffer pool is determined, there is a need to set a dividing ratio by which the memory area is divided into a plurality of buffer pools to a suitable value. However, it is difficult to calculate a dividing ratio at which the access speed is maximized. Further, in some cases of access to a database, it is preferable to dynamically change the dividing ratio, depending on characteristics of access.
The following documents are considered:                [Patent Document 1]        Published Unexamined Patent-Application No. 9-330256        [Non-Patent Document 1]        Y. Diao et al., “Generic Online Optimization of Multiple Configuration Parameters With Application to a Database Server”, pp. 3-15, Lecture Notes in Computer Science 2867, Springer, 2003.        
In view of these problems, a method has been proposed in which the dividing ratio is calculated by substituting statistical information such as a record of use of a buffer pool in a predetermined mathematical expression (see Patent Document 1). In this method, the mathematical expression is determined in advance on the basis of user's experience, knowledge and the like.
Another method has been proposed in which the dividing ratio is determined on the basis of a direct search method (see Non-Patent Document 1). In this method, a plurality of dividing ratios different from each other are first set on the basis of a search algorithm, and an average response time is measured. The same steps are repeated to make a plurality of dividing ratio settings and measure average response with respect to the dividing ratio settings until a minimum average response time is obtained.
The following problems are to be solved by the invention:                According to Patent Document 1, it is difficult to set a suitable mathematical expression by supposing all possible access patterns. Moreover, in some cases where the pattern of access to a database is changed, it is unsuitable to continue using the same mathematical expression. For this reason, it is thought to be difficult to apply one mathematical expression to a general-purpose database server capable of processing according to various requirements.        According to Non-Patent Document 1, many candidates exist for the next dividing ratios to be set after measurement of one average response time. It is difficult to set suitable dividing ratios by selecting from the candidates by a small number of searches.        